Using the DebuggerTypeProxy

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Using the DebuggerTypeProxy

Use the DebuggerTypeProxyAttribute attribute when you need to significantly and fundamentally change the debugging view of a type, but not change the type itself. The DebuggerTypeProxyAttribute attribute is used to specify a display proxy for a type, allowing a developer to tailor the view for the type. This attribute, like the DebuggerDisplayAttribute, can be used at the assembly level, in which case the Target property specifies the type for which the proxy will be used. The recommended usage is that this attribute specifies a private nested type that occurs within the type to which the attribute is applied. An expression evaluator that supports type viewers checks for this attribute when a type is displayed. If the attribute is found, the expression evaluator substitutes the display proxy type for the type the attribute is applied to.

When the DebuggerTypeProxyAttribute is present, the debugger variable window displays only the public members of the proxy type. Private members are not displayed. The behavior of the data window is not changed by attribute-enhanced views.

To avoid unnecessary performance penalties, attributes of the display proxy are not processed until the object is expanded, either through the user clicking the plus sign (+) next to the type in a data window, or through the application of the DebuggerBrowsableAttribute attribute. Therefore, it is recommended that no attributes be applied to the display type. Attributes can and should be applied within the body of the display type.

The following code example shows the use of the DebuggerTypeProxyAttribute to specify a type to be used as a debugger display proxy.
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[DebuggerTypeProxy(typeof(HashtableDebugView))]
class MyHashtable : Hashtable
{
    private const string TestString =
        "This should not appear in the debug window.";

    internal class HashtableDebugView
    {
        private Hashtable hashtable;
        public const string TestStringProxy =
            "This should appear in the debug window.";

        // The constructor for the type proxy class must have a
        // constructor that takes the target type as a parameter.
        public HashtableDebugView(Hashtable hashtable)
        {
            this.hashtable = hashtable;
        }
    }
}



Source : MSDN